Government experts believe there is still a risk of people contracting variant Creutzfeldt-Jakob Disease (vCJD) through blood transfusions, as about 30,000 Britons are likely to be carrying the brain-wasting illness in a dormant form — double the previous estimate.

They warn the current total death toll of 176 from vCJD could rise more than five-fold as the infection has not been wiped out of the blood supply like it has been in the food chain.

Frank Dobson, a former health secretary, tonight urged ministers to develop a nationwide screening programme for blood donors to stop future infections of vCJD, which has the potential to cause “horrendous deaths”.

People are no longer in danger of getting vCJD from eating British beef, after ministers ordered the slaughter of millions of cows when the “mad cow” disease scandal broke in 1989. Fears that hundreds of thousands of people could contract the human form of bovine spongiform encephalopathy (BSE) proved unfounded.

However, the Government acknowledges that one in 2,000 Britons – or approximately 30,000 people- are already “silent” carriers of infectious proteins that lead some people to develop vCJD.

A little-reported study last summer concluded the prevalence of this “silent” vCJD is likely to be twice as high as previously thought.

These 30,000 carriers can unknowingly pass on the infectious proteins – known as prions – to new potential sufferers through donated blood.

Because so little is known about vCJD, there is no telling which carriers will go on to develop the disease or whether any new cases will actually materialise at all.

There have been no new cases for two years and there are thought to be no surviving sufferers of vCJD, which has always historically proved fatal.

However a new risk assessment published this month by the Government’s Health Protection Analytical team reveals that infected blood donations could cause up to 1,000 deaths in a high case scenario.

About half of the cases could develop in people who have already received blood transfusions and up to 580 cases from people who are yet to be infected with the disease. The central estimate of infections yet to occur is 205.

It suggests ministers could consider recruiting young blood donors born after 1996 once they become eligible, as they will not have eaten infected beef.

“The number of “silent” vCJD infections associated with transfusion would be much higher than the number of clinical cases,” it said. “It is therefore important to maintain, and if possible enhance, measures to prevent onward transmission of infection, notably the exclusion of recipients from donating blood.”

Mr Dobson, the former Labour Health Secretary, said “everything humanly possible should be done to develop a blood test”.

“There is no room at all for complacency,” he told The Daily Telegraph. “With a blood test, you would be able to screen every potential donor. If that screening showed the incidence was higher than thought then maybe you would do it for the whole population.”

Professor John Collinge, an expert from University College London, whose research unit has developed a blood test for vCJD, said there is an element of “wishful thinking” within the Government, with officials hoping the problem has gone away.

He said he is “sceptical of guesstimates” of future cases and believes ministers need to start a study of vCJD in blood, rather than appendices, to get a proper grip on the risk of infection through transfusions.

“The figure of one in 2,000 in the appendix study was pretty worrying,” he said. “I was pretty alarmed by that. It’s clear there is a very substantial pool of infection in the community. There needs to be blood testing to answer this question of prevalance properly.”

Sir Paul Beresford, an MP and former Conservative environment minister, also believes the Government must wake up to the potential for future vCJD infections and is campaigning for more filtering of donated blood.

“If we’ve got it wrong our grandchildren are going to potentially have an epidemic of vCJD that we can do nothing about but we can prevent it if we act now,” he said.

“There’s some quite simple things they can do. For example, there’s a new system that’s being developed that will filter red blood cells before transfusion.

“[The system] is not adequate at the moment but the Government’s argument is that there’s no sign of a risk because the number of people turning up with vCJD is going down. But it can take 10, 15, 20, 25 years for this to pop up.”

A spokesman for the Department of Health said the Government continues to encourage “people of all ages to give blood”, adding “we have one of the safest blood supplies in the world”.

“Independent experts from the Advisory Committee on the Safety of Blood, Tissues and Organs have used this study during their considerations of measures to reduce the potential risk of transmission through blood transfusions,” she said. “There is no evidence of any UK clinical cases of vCJD being linked to a blood transfusion given after 1999.

“In fact there have been no new cases in the UK for more than two years.”

She said the study relates to people’s future potential to develop vCJD, not actual new cases that have occured.